D’YOUVILLE COLLEGE
BIOLOGY 108/508 - HUMAN ANATOMY & PHYSIOLOGY II
LECTURE # 23
BODY FLUID PHYSIOLOGY
ACID-BASE BALANCE
1.
Acids, Bases and Buffers:
a. Acids: yield hydrogen ions in solution; concentration: # of moles/liter;
strength: degree of ionization (extent of H+ yield)
• strong acids typically are mostly ionized yielding the maximum # of H+:
HCl <- ---------> H+ + Cl• weak acids will be mostly non-ionized yielding small # of H+:
HA <-------- --> H+ + A• respiratory acid: carbon dioxide forms weak acid in water (carbonic acid)
• all other sources of hydrogen ions (e.g. lactic acid, hydrochloric acid, ketone
bodies) are metabolic acids
b. Bases: consume hydrogen ions from solution; the anion portion of an ionized
acid is known as conjugate base
c. Buffers: systems of weak acid + acid anion which react to offset changes in
hydrogen ion concentration of a solution; increasing acidity causes buffer system to
behave as a base; decreasing acidity causes buffer system to behave as an acid
• Bicarbonate System: mostly associated with extracellular fluid; important
because of linkage to respiratory and renal influences on pH
H2O + CO2 <-- * --> H2CO3 <-------- ---> H+ + HCO3* = carbonic anhydrase enzyme
• Protein System(s): highest concentration; mostly intracellular (e.g.
hemoglobin oxygenation reaction)
NPrCOOH <-- -->H+ + +H3NPrCOO-<-- --> 2H++ H2NPrCOO• Phosphate System: mostly intracellular, also important in renal tubules
H3PO4 <-- -->H+ + H2PO4-<-- --> 2H+ + HPO42• Ammonia: mainly renal tubules
NH4+ <-- --> H+ + NH3
2.
Body Fluid pH:
• intracellular fluid (cytoplasm) - normal pH = 7.0
• extracellular fluid (plasma, interstitial fluid) has normal pH = 7.4
• pHECF > 7.45 constitutes alkalosis; pHECF < 7.35 constitutes acidosis
• alkalosis causes hyperactivity of nervous system (convulsions)
• acidosis causes depression of nervous system (coma)
• changes in PCO2 (high -> resp. acidosis; low -> respiratory alkalosis)
• changes in other acids (high = metab. acidosis; low = metabolic alkalosis)
• changes caused by HCO3- (low = metabolic acidosis; high = metabolic
alkalosis)
Bio 108/508
3.
lec. 23 - p. 2
Defenses Against pH Changes:
a. Buffers: systems interact to maintain pH between 7.35 - 7.45
b. Respiratory Adjustment:
• hyperventilation blows off CO2 causing shift in bicarbonate system that
consumes more H+ (alkalinizing effect, higher pH)
• hypoventilation accumulates CO2 causing shift in bicarbonate system that
elevates H+ (acidifying effect, lower pH)
c. Renal Adjustment: kidneys secrete hydrogen ion (tubular secretion) in
conjunction with bicarbonate absorption
• Correcting Acidosis: kidneys secrete more H+ and retain more bicarbonate
ion (bolstering buffer system)
• Correcting Alkalosis: kidneys retain H+ and excrete more bicarbonate ion